Description:
<jats:title>Abstract</jats:title><jats:p>Cyclic silylated chalconium borates <jats:bold>13</jats:bold>[B(C<jats:sub>6</jats:sub>F<jats:sub>5</jats:sub>)<jats:sub>4</jats:sub>] and <jats:bold>14</jats:bold>[B(C<jats:sub>6</jats:sub>F<jats:sub>5</jats:sub>)<jats:sub>4</jats:sub>] with <jats:italic>peri</jats:italic>‐acenaphthyl and <jats:italic>peri</jats:italic>‐naphthyl skeletons were synthesized from unsymmetrically substituted silanes <jats:bold>3</jats:bold>, <jats:bold>4</jats:bold>, <jats:bold>6</jats:bold>, <jats:bold>7</jats:bold>, <jats:bold>9</jats:bold> and <jats:bold>10</jats:bold> using the standard Corey protocol (Chalcogen Ch=O, S, Se, Te). The configuration at the chalcogen atom is trigonal pyramidal for Ch=S, Se, Te, leading to the formation of <jats:italic>cis</jats:italic>‐ and <jats:italic>trans</jats:italic>‐isomers in the case of phenylmethylsilyl cations. With the bulkier <jats:italic>tert</jats:italic>‐butyl group at silicon, the configuration at the chalcogen atoms is predetermined to give almost exclusively the <jats:italic>trans</jats:italic>‐configurated cyclic silylchalconium ions. The barriers for the inversion of the configuration at the sulfur atoms of sulfonium ions <jats:bold>13 c</jats:bold> and <jats:bold>14 a</jats:bold> are substantial (72–74 kJ mol<jats:sup>−1</jats:sup>) as shown by variable temperature NMR spectroscopy. The neighboring group effect of the thiophenyl substituent is sufficiently strong to preserve chiral information at the silicon atom at low temperatures.</jats:p>